1. Field of the Invention
The present invention relates to a vaccine prepared from Mycoplasma hyorhinis isolated from the lung lesions of pigs infected with enzootic pneumonia and the application of the foregoing vaccine.
2. Description of Related Art
Swine enzootic pneumonia is a chronic disease characterized by high infection rate and low mortality that infects 25˜93% of swine herds and is positive in 28˜80% of lung tissues of carcasses. The growth efficiency of infected pigs is reduced by 14˜16%. In high-density rearing environment that is poorly ventilated and moist with wildly changing climate, the incidence and spread of swine enzootic pneumonia can rise to an alarming level, resulting in lower feed conversion, regarded growth, inflammatory reaction and immunosuppression in pigs. This disease is often accompanied by secondary infection of opportunistic pathogens, such as Actinobacillus pleuropneumoniae, Pasteurella, and Streptococcus suis, leading to serious economic loss and becoming one of important reasons for the cost increase of the pig industry.
The strategic approach to the prevention of swine enzootic pneumonia in Taiwan is to add antibiotic in the feed. But long-term use of antibiotic is prone to produce resistant strains and leads to the problem of residual antibiotic in the meat products, which poses significant health issue. Field experience also shows the preventive effect of feeding animals with drugs is not as ideal as expected.
There are three commonly seen mycoplasma in pigs, which are Mycoplasma hyopneumoniae (M. hyopneumoniae), Mycoplasma hyorhinis (M. hyorhinis), and M. flocculate. M. hyopneumoniae is the important causative organism of swine enzootic pneumonia (SEP); M. hyorhinis is the etiological agent of polyserositis and arthritis; M. flocculate has not been shown to cause diseases. In the past, all SEP incidences were caused by M. hyopneumoniae. But recently it is found that such disease is caused by either M. hyorhinis alone or the combination of M. hyorhinis and M. hyopneumoniae. In Taiwan, mycoplasma isolated from the lung lesions of pigs infected with SEP was only M. hyopneumoniae prior to 1996. In the case reports in other countries, M. hyorhinis was primarily isolated from the synovial fluid of pigs infected with arthritis, which did not cause SEP and was not considered an important pathogen for swine diseases. Taiwan never isolated this pathogen in the past. But starting in 1996, the Mycoplasma Laboratory of Animal Technology Institute Taiwan finds mycoplasma isolated from the lung lesions of pneumonia-infected pigs to be M. hyorhinis in more incidences as confirmed by antibody binding reaction using Western blotting and comparison with ATCC standard strains.
The Animal Technology Institute Taiwan provides mycoplasma isolation and identification service to pig farms around the country, and sees higher and higher incidence of M. hyorhinis isolates from pneumonia cases. In the 242 cases in 2001 and 205 cases in 2002, the M. hyopneumoniae infection rate dropped from 46.8% in 2001 to 15.8% in 2002, while that of M. hyorhinis rose from 65.5% in 2001 to 79.2% in 2002. The infection rate of the mixture of M. hyopneumoniae and M. hyorhinis was 14.4% in 2001 and 15% in 2002. These figures indicate rapidly rising M. hyorhinis infection in swine pneumonia cases in Taiwan and rapidly dropping infection rate of M. hyopneumoniae, while infection rate of the mixture of the two remains steady. It also indicates that M. hyorhinis is gradually replacing M. hyopneumoniae as the most significant pathogen of SEP. The past belief was that M. hyopneumoniae was the only species among mycoplasma to cause SEP. This is not the situation now. In the isolation cases described above, there was one pure M. hyorhinis infection case in 2001, and five such cases in 2002, suggesting M. hyorhinis alone could elicit SEP.
Field experience shows that the chance of reinfection with the same mycoplasma species is relatively low, indicating good innate immunity of the pigs against such pathogen. Thus using vaccination as a means of disease prevention is a viable approach. Given the weak cross reaction between the antigens of M. hyorhinis and M. hyopneumoniae, it is found in pig farm survey on vaccination that pigs administered with M. hyopneumoniae vaccine were not effectively protected against the infection of M. hyorhinis. For pigs infected with both mycoplasma species, the effect of administering M. hyopneumoniae vaccine or M. hyorhinis vaccine alone was not satisfactory. Only vaccine containing the mixture of both mycoplasma antigens provides adequate protection. Thus developing vaccine containing M. hyorhinis or both M. hyorhinis and M. hyopneumoniae is a pressing task.